Musnad Ahmad 1156:127

'Abd al-Razzaq narrated to us, he said: Sufyan narrated to us, from Abu Ishaq, from Abu Salamah ibn 'Abd al-Rahman, from Umm Salamah, she said: By the One who took his soul—meaning the Prophet, may God bless him and grant him peace—he did not pass away until most of his prayer was while sitting, except for the obligatory ones. And the most beloved of deeds to him was that which the servant persists in, even if it were little.